Viscosity monitor



United States Patent 3,234,781 VKSCOSITY MONITOR Charles E. Bragg,Lansing, 111., assignor to Standard Oil Company, Chicago, 111., acorporation of Indiana Filed Mar. 20, 1963, Scr. No. 266,705 8 Claims.(Cl. 73-55) This invention relates to viscosimeters and moreparticularly concerns the provision of a continuous viscosimeter havingutility in monitoring high speed, lubricant oil, canning operations.

In the canning of lubricant oils, high speed machines are set up to cana certain quantity of a particular product. Usually a single run will beof several hours duration. The composition of the lubricant oil is knownto be correct at the start of a run, but there are many factors whichcould, and on past occasions have, resulted in a change of compositionand a quantity of canned ofispecifications material. Since such changesare rarely known before the end of the run, it is necessary to scrap allof the product canned during the run. There is a further problem in oilcanning operations. When changing from one grade of oil to another, itis conventional to flush out the equipment with fresh oil. Flushing mustbe completed before a new run can begin, or else the initial cans willbe contaminated with oil from a previous batch. It has heretofore beenthe practice to continue flushing for a fixed period of time known to besufficient, but this almost invariably entails an arbitrary-anduncertain-choice between under-flushing, with the possibility ofcontamination or over-flushing, with the certainty of waste.

According to the invention, there is provided a simple viscositymonitoring apparatus which permits constant and instantaneousdetermination of oil viscosity. As a result, departures from viscosityspecifications are detected instantaneously and the canning equipmentcan be shut down without need for scrapping the entire lot. In addition,the apparatus permits inspection of the flushing operations so that thecontamination of under-flushing and the waste of over-flushing areavoided.

The inventive apparatus essentially comprises a simplified viscosimeterof the type in which a fluid at constant pressure and temperature flowsthrough a fixed restriction, and the pressure drop across thisrestriction is determined as a measure of fluid viscosity. The pressuredrop in the inventive apparatus is obtained with a pressure-sensitiveelectrical resistance element, or transducer, which constitutes onebranch of a Wheatstone bridge circuit. An other branch is an adjustableelectrical resistance, which is used in setting the bridge for aspecified viscosity product.

To detect minimum and maximum limits of bridge imbalance correspondingto a permissible viscosity range, the Wheatstone bridge may be alsoequipped with a meter relay which actuates an audible or visible alarmsignal when the bridge is exceptionally out of balance, i.e., when theproduct viscosity is lower or higher than that specified. These limits,as well as the viscosity specification itself, may be adjusted at will.As indicated earlier, a particular advantage of the inventive apparatusis its simplicity. In one embodiment, an oil preheater, a constantvolume pump, and the fixed restriction are all disposed within a vesselthat is heated with saturated steam. Thus, all of the mechanicalcomponents of the inventive apparatus are held at constant temperature.

The invention, in its various aspects, will be described in furtherdetail, and additional features and advantages thereof will become moreapparent, in the ensuing specification which is to be read inconjunction with the attached figures wherein:

3,234,781 Patented Feb. 15, 1966 FIGURE 1 is a schematic representation,partially in section, of the mechanical components of the invention; and

FIGURE 2 is a circuit diagram of the electrical components of theinvention.

Turning first to FIGURE 1, conduit 11 withdraws a sample stream ofliquid passing through conduit 12 from a reservoir to the canningmachine. Conduit 11 is provided with a pressure control valve 13 tomaintain constant downstream pressure leading to the viscosimeter.

The viscosimeter comprises a vessel 14, having a bottom cylindricalsection 16 and a top flanged section 17, the two sections being boltedtogether via bolt holes 18 and bolts, not shown. Gasket 19 affordspressure tightness.

Vessel 14 is provided with several access and egress conduits. Steam, atlow pressure and saturated, is admitted via conduit 21, while condensateis withdrawn via conduit 22 at the bottom of vessel 14.

Oil from conduit 11 enters vessel 14 and flows in sequence to a coiledtube preheater 23 (suitably 15 ft. in total length and having Ms outerdiameter and 0.015" inner diameter), a constant volume pump 24, a fixedrestriction 26 (suitably 34" of /s" OD. x 0.065" IJD. tubing) and thencedischarges via outlet conduit 27. Pump 24 is suitably a gear pump whichdelivers a substantially constant volume independent of upstream and/ ordownstream pressure; pump 24 is driven via shaft 28 (passing throughbearing 29) and synchronous motor 31 The pressure drop acrossrestriction 26 (shown coiled in the figure) is determined by apressure-sensitive electrical resistance element 32, or transducer T.Such transducers are well known, and constitute a flexible diaphragm orbellows which actuates the wiper arm of a potentiometer. The oppositeside of electrical resistance element 32 is connected to the atmosphere,that is, to the same pressure region that outlet conduit 27 discharges.For convenience, an auxiliary pressure gage 33 may be connected into thesame conduit 34 to which the electrical resistance element 32 isconnected.

Turning now to FIGURE 2, the electrical circuitry is shown in schematicview. Line voltage is taken via terminals 35 at volts, 60 cycle. It isbrought to a low voltage isolation transformer 36 and thence to a singlewave rectifier consisting of resistance 37, rectifier diode 38, andcapacitor 39 (450 volts, 20 microfarad). The rectifier current, atroughly 6.3 volts, is then conducted to a voltage divider composed ofresistance 41 (1,000 ohms) and resistance 42 (500 ohms).

The Wheatstone bridge is powered from taps 43 and 44 of the voltagedivider and receives about 3 volts pulsating DC.

The Wheatstone bridge comprises two branches of fixed resistance,resistors 46 and 47 (SK each), one variable resistance 48 (a 5K Helipotpotentiometer), the pressure-sensitive electrical resistance 32, and thebalancing potentiometer 49 (1K Helipot potentiometer). Variableresistance 48 serves as a memory unit, storing a resistance valuecorresponding to the viscosity of a sample known to be correct at thestart of a run; the bridge thus compares the instantaneous viscositywith this stored viscosity. To facilitate adjustment of variableresistance 48, or to enable the balanced bridge to measure an unknownviscosity, it may be provided with a dial calibrated to read viscosity.

The galvanometer 51, shunted with a 500 ohm resistance 52 and with astabistor (Zener diode) 53 for overload protection, is a meter relayhaving both minimum and maximum contacts 54 and 56, both of which areadjustable so as to permit variation of the permissible imbalance of theWheatstone bridge.

Galvanometer 51 will ordinarily read at zero when the bridge isbalanced, but will contact terminals 54 or 56 should imbalance exceed apredetermined minimum or maximum limit.

Contact terminals 54 and 56 of galvanometer 51 are connected togetherand thence communicate with a double-contact double-locking relay 57.Relay 57 is connected into the power line via lines 58, and has one setof contacts 59 which are normally closed when the Wheatstone bridge isbalanced; when the bridge is balanced (more accurately, when no contactis being made with contact terminals 54 or 56 of galvanometer 51), thegreen signal light 61 is lit, signifying a satisfactory range ofviscosities. However, when contact terminals 54 or 56 are closed,contact 62 on relay 57 engages contact 63 on relay, thereby breaking thecircuit to green light 61 and closing the circuit to the amber light 64,signifying unsatisfactory viscosity. To release the locking action ofrelay 57, a normally closed push button switch 66 is provided; this mustbe open to return the light from amber to green when a satisfactoryviscosity is restored.

In addition to, or in place of, the visible signal lights 61 and 64, anaudible alarm signal may be used which sounds an alarm when thepermissible viscosity range is no longer maintained.

To employ the inventive system, oil is admitted from conduit 12 throughconduit 11, preheater 23, pump 24, and flow restriction 26. In the usualcase, potentiometer 48 and/ or 49 are adjusted to bring the Wheatstonebridge into balance, and push button 66 is engaged to turn on greenlight 61. Canning is then commenced and lubricant oil flowing throughconduit 12 is continuously sampled. Should there be no variation in oilviscosity (beyond the range normally provided for by adjustment ofcontacts 54 and 56 on galvanometer 51) the light 61 remains greenthroughout the entire run.

However, should there be a departure from permissible minimum or maximumviscosity, then contacts 54 or 56 are engaged, which actuates relay 57and switches the light from green 61 to amber 64. At the same time, analarm may ring if such has been provided. The operator may then turn offhis canning machine, discarding only th: last few cans, and resumingoperation after he has ascertained the cause of the viscosity departureand has rectified the same.

At the conclusion of one canning run, and when it is desired to switchto an oil of different viscosity, potentiometer 48 is readjusted to apredetermined setting (to be illustrated subsequently) and a new gradeof oil is passed from the reservoir through conduit 12 and thence toviscosimeter via valved conduit 11. By observing the dial ongalvanometer 51, the operator can immediately determine when sufiicientflushing has occurred so that the oil currently involved through conduit12 is suitable for canning; when this takes place, galvanometer 51 willbe balanced.

To adjust potentiometer 48 it is merely necessary to calibrate thepotentiometer 48 from previous runs with oils of known viscosity. Thecorrelation between an oil viscosity recorder setting is generallylinear, and hence only two calibration points are necessary. Also, byusing oils of known viscosity, the adjustments of contacts 54 and 56 ongalvanometer 51 may be adjusted to ascertain the minimum or maximumpermissible ranges of viscosity.

From the foregoing description, it is evident that there has beenprovided, in accordance with the invention, a simple rugged, andfoolproof apparatus for detecting viscosity departures in a fluid.Although the inventive apparatus is especially suited for use inconjunction with canning of lubricant oils, it is evident that it hasmany other uses, e.g. continuous viscosity monitoring of various oilrefinery and chemical plant streams.

Further, while the invention has been described in conjunction withspecific embodiments thereof, these are for illustrative purposes only,and many alternatives, modifications and variations will become apparentto those skilled in the art in light of the foregoing description. It istherefore intended to embrace all such alternatives, modifications andvariations as fall within the spirit and broad scope of the appendedclaims.

I claim:

1. In a viscosimeter which may be used to monitor the viscosity of aflowing liquid stream and which is of the type wherein a fluid atconstant pressure and temperature flows through a fixed restriction andwherein the pressure drop across said restriction is determined as ameasure of fluid viscosity, the combination comprising: apressure-sensitive electrical resistance for determining said pressuredrop; a Wheatstone bridge circuit having said electrical resistance asone branch thereof and having an adjustable electrical resistance asanother branch thereof; means for detecting minimum and maximum limitsof bridge imbalance corresponding to a permissible viscosity range; andmeans responsive to said detecting means for signaling departures fromsaid permissible viscosity range.

2. Viscosimeter of claim 1 wherein said fixed restriction, a constantvolume pump upstream of said fixed restriction, and a heat exchanger areall disposed within a constant temperature vessel.

3. The viscosimeter of claim 2 wherein said vessel is maintained atconstant temperature by introducing steam therein.

4. The viscosimeter of claim 1 including means for adjusting the minimumand maximum limits of bridge imbalance.

5. The viscosimeter of claim 1 including overload-responsive means forshorting out said detector means at excessive bridge imbalance.

6. The viscosimeter of claim 1 wherein said signaling means comprises acolored light, said light having a color different from a second lightindicating viscosity to have said permissible viscosity range.

7. A continuous viscosimeter comprising a constant temperature vesselhaving provisions for admitting steam therein and for withdrawingcondensate therefrom; a conduit having the pressure-controlling valvetherein for receiving a fluid sample; a heat exchanger within saidvessel and communicating with said conduit; a constant volume pumpwithin said vessel disposed downstream of said heat exchanger; a flowrestriction disposed downstream of said constant volume pump anddischarging fluid externally of said vessel; a pressure-sensitiveelectrical resistance for measuring the pressure drop across said flowrestriction; a Wheatstone bridge including said electrical resistance asone branch thereof and having an adjustable electrical resistance asanother branch thereof; means for detecting minimum and maximum limitsof bridge imbalance corresponding to a permissible viscosity range; andmeans responsive to said detecting means for signaling departures fromsaid permissible viscosity range.

8. The viscosimeter of claim 7 including means for adjusting the minimumand maximum limits of bridge imbalance.

References Cited by the Examiner UNITED STATES PATENTS 2,539,892 1/1951Cook 73-398 X 2,834,200 5/1958 Rhodes et al. 7355 3,115,768 12/1963Rhodes et al. '7355 3,116,630 l/l964 Piros 7355 3,127,586 3/1964 Heyn eta1 340240 X LOUIS R. PRINCE, Primary Examiner.

DAVID SCHONBERG, Examiner.

1. IN A VISCOSIMETER WHICH MAY BE USED TO MONITOR THE VISCOSITY OF AFLOWING LIQUID STREAM AND WHICH IS OF THE TYPE WHEREIN A FLUID ATCONSTANT PRESSURE AND TEMPERATURE FLOWS THROUGH A FIXED RESTRICTION ANDWHEREIN THE PRESSURE DROP ACROSS SAID RESTRICTION IS DETERMINED AS AMEASURE OF FLUID VISCOSITY, THE COMBINATION COMPRISING: APRESSURE-SENSITIVE ELECTRICAL RESISTANCE FOR DETERMINING SAID PRESSUREDROP; A WHEATSTONE BRIDGE CIRCUIT HAVING SAID ELECTRICAL RESISTANCE ASONE BRANCH THEREOF AND HAVING AN ADJUSTABLE ELECTRICAL RESISTANCE ASANOTHER BRANCH THEREOF; MEANS FOR DETECTING MINIMUM AND MAXIMUM LIMITSOF BRIDGE IMBALANCE CORRESPONDING TO A PREMISSIBLE VISCOSITY RANGE; ANDMEANS RESPONSIVE TO SAID DETECTING MEANS FOR SIGNALING DEPARTURES FROMSAID PERMISSIBLE VISCOSITY RANGE.